Cathode-ray storage tube apparatus and method of operation



Oct.

Filed Aug. 30, 1946 P. K. WEIMER ETAL CATHODE-RAY STORAGE TUBE APPARATUSAND METHOD OF OPERATION 6 Sheets-Sheet 1 Oct. l2,

Filed Aug.

TRA Ns. I Ifp uz 6E 1948. P. K. wElMER ETAL 2,451,005

CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION 30, 1946 6Sheets-Sheet 2 Rec. El' g TRM/s Rfc, fifa/sf WFM/1.55 I/Pz/Lsf I I L/GH7' PULSE l I l 2L I scfPff/v Porn/TML 7M l Jamin aap/N6 2m scm/uwsIRv/NG WULFF A T TOR/VE Y Y Oct. 12, 1948. P. K. WEIMER ETAL(CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION 6Sheets-Sheet -3 asm oscopf ELAN/'50 LIGHT Arm/'mfr Oct. 12, 1948. P. K.wElMER Erm. 2,451,005

CATHODE-RAY STORAGE TUBE APPARATUS AND METHOD OF OPERATION Filed Aug.30, 1946 6 Sheets-Sheet 5 /MAGE ORTH/CO/V FOR TIME DEX 7G/VAL //V 7'RGDUCED U JCREEA/ PULSE F11/sf I IPUTOW/V I mlm-@FF I 55AM Guxme-Nr I/3/ I--I (//vpur .WGA/,4.4) |/\/I I /32 I l I I I (33 |V I r/MfPOTENTIAL 0F 2 I-z----I l /36 ,vorf/vT/AL'MFT a/v GLASS TARGET FORTARGET Br 1:1.' suiv (BEFORE SCA/v) RE Tuk/v 55AM (our/ur S16/VAL) 1NVEN TOR. PAUL A. WE/MEE' VLAD/M/R A. Z WOR YK /N da ATTUR/VEY K.wl-:IMER er AL 2,451,005 AY STORAGE TUBE APPARATUS @cte P.

cA'rHonE-R AND METHOD or' OPERATION Filed Aug. so, 1946 e sheets-sheet 6PULJL SQUARE PULSE E' GLA/MA1 R WAVE- i SOURCE j GIA/5R47' "5) /2/ y L5356/ REVERS/N6 U5) r "N L 4 VL AMP. :LJ-11144 m r 61 "7 l, AMR r\fS16/VAL? 36N DEFL. INPUT c/RcU/ V will 46 2/ /34 54) n.9` :aU/verafLIGHT PULSE OUTPUT L\ AMR P- AMP s/GNAL INPUT URV/N6 WoLFF atented Oct.12, 19

CATHGDE-RAY STORAGE TUBE APPARATUS AND METHOD F OPERATION Paul K. Weimerand Vladimir K. Zworykin, Princeton, and Irving Wolil, Manasquan, N. J.,assignors to Radio Corporation of America, a

corporation of Delaware Application August 30, 1946, Serial No. 694,042

1s claims. 1

Our invention relates to cathode ray storage tube apparatus andparticularly to methods of and means for utilizing such apparatus forground clutter reduction in radar systems, for delaying signals, etc.

The invention will be described with particular reference to the use ofa television pick-up tube of the type known as the Image Orthiconespecially as applied to a radar system for distinguishing betweenstationary and moving objects. One of the diiliculties in detectingaircraft approaching a radar station, particularly if the aircraft is ata low altitude, is that the signal reflected from the ground or frombuildings or hills obscures the signal reflected from the aircraft. Suchobscurlng signals are referred to as ground clutter. Similarly, signalreflected from an aircraft flying through a regionfilled with floatingmetal foil or the like may be obscured by reflections from the metalfoil.

One of the objects of the present invention is to provide an improvedmethod of and means for distinguishing between signals reflected fromstationary or substantially stationary objects and signals reflectedfrom moving objects.

A further object of the invention is to provide .an improved method ofand means for reducing the amount of ground clutter or the like in aradar picture.

A still further object of the invention is to provide an improved methodof and means for utilizing a cathode ray storage tube of thelow-velocity-beam double-sided-mosaic type for distinguishing betweensignals reflected from stationary objects and signals reected frommoving objects.

.A still further lobject of the invention is to provide an improvedmethod of and means for utilizing a cathode ray storage tube of thelow-velocity-beam double-sided-mosaic type for delaying signals.

Y A still further object of the invention is to provide an improvedmethod of and means for indicat-.ing any difference in signals thatoccur in succession.

According to one preferred embodiment of the invention, a cathode raystorage tube of the Image Orthicon type is employed in combination witha. pulse-echo radar system of the coherent pulse type. By utilizinga'coherent pulse system the phase of the carrier wave of the ref'lectedpulse may be compared with a carrier wave of fixed phase so that anychange in phase due to motion of the reflecting object may be detected.Thus, there may -be supplied to the 2 storage tube a received signalthat remains the same for successive received pulses if the pulses arereilected from a stationary object but which is dlerent for eachreceived pulse if the reilecting object is moving. The storage tube isemployed for comparing the successive signals and is so operated thatthere is signal output only if successive signals are unlike.

In this embodiment of the invention for distinguishing betweenstationary and moving objects, the successive signals from the radarreceiver or mixer are applied to a storage tube electrode so that onesignal puts a charge pattern on the storage plate or target as itisscanned by an electron beam. If the next successive signal (produced bythe next reflected pulse) is the same there will be no output signal butif it is different there will be an output signal or pulse indicatingreilection from a moving-object. At the end of the second signal (andthe second electron beam scan) light is flashed on the photocathode ofthe storage tube to bring the tube back to its initial operatingcondition.

The invention will be better Iunderstood from the following descriptiontaken in connection with the accompanying drawing in which Figure l is ablock and circuit diagram showing one embodiment of the invention asapplied to a pulse-echo radar system of the coherent pulse type whereinthe signa-ls are impressed upon a mesh screen electrode of the storagetube,

Figure 1A is a view illustrating a modiilcation of the circuit shown inFig. 1 wherein the signals are impressed upon the cathode of the storagetube,

Figure 2 is a group of graphs that illustrate the operation of theapparatus of Fig; 1 when successive receivedsignals are alike.

Figure 3 is a group of graphs that illustrate the operation of theapparatus of Fig. 1 when successive received signals are dilerent aswhen reflected from a moving object,

Figure 4 is a block and circuit diagram of an embodiment of theinvention wherein the received signal is applied to a control electrodeof the storage tube to modulate the electron beam of the storage tubeinstead of being applied to a screen adjacent to the target plate as inFig. l or to the cathode as in Fig. 1A,

Figure 5 is a group of graphs that illustrate the operation of theapparatus of Fig. 4,

Figure 6 is a group of graphs that illustrate the use of the inventionfor delaying a signal where the signal is applied to the screen adjacentto the target plate,

Figure 7 is a group oi graphs that illustrate the use of the inventioni'or delaying a signal when the signal is applied to the electron beammodulating electrode, and

Figures 8 and 9 are block and circuit diagrams illustrating apparatusfor delaying a signal in the way illustrated in Figs. 6 and '7,respectively.

In the several figures similar parts and similar graphs are indicated bysimilar reference characters.

Referring to Fig. 1, the radar system includes a radio pulse transmitterwhich comprises an oscillator I acting as a source of radio frequencyenergy and a power amplifier II which is pulse Y modulated by means ofperiodically recurring pulses supplied from a pulse generator I2 througha suitable modulating circuit I3. As inthe usual pulse-echo systems, theresulting radio pulses radiated from the transmitter antenna i6 are ofshort duration compared with the period be-V tween successive pulses.

Pulses reflected from an object are picked up by a receiving antenna I1and supplied to a mixer I8 which may be the same as the first detectoror converted tube of a superheterodyne receiver. However, the localoscillator signal supplied to the mixer I 8 is obtained from the R.F.source I0 and is of the same'frequency as Athe carrier wave of thereceived signal.

The output signal of the mixer I8 depends upon the phase relation of thereceived carrier wave signal with respect to the R.F. signal suppliedfrom the source I0 to the mixer. This output signal is the same forsuccessive received pulses of R.F. signal so long as this phaserelationis unchanged, as when the signal is reilected from stationaryobiects.However, if the reecting object is moving, the said phase relation iscontinuously changing and the mixer output signal is dierent for eachreceived pulse.

In order to detect a changing signal and separate it from any unchangingsignal, a cathode ray storage tube 2| is employed. The specific storagetube shown is the well known Image Orthicon which comprises adouble-sided mosaic or target plate 22 on which signal is stored, a meshscreen electrode 23 close to the target plate 22, and a photoelectriccathode 24 on'the large end of the tube envelope. The tube 2l furthercomprises an electron gun at the other end of the tube envelope whichcomprises a cathode 26, a control electrode 21. and a ilrst anode 28. Astorage tube of the Image Orthicon type is described in applicationSerial No. 554,494, led September 16, 1944 in the name of Paul K.Weimer, and `which is now U. S. Patent 2,433,941, issued Jan. 6, 1948.

The storage tube 2| is also provided with a w coating 29 that is held ata potential less than that of the anode 28 and is further provided witha ringelectrode 3| that is at ground potential. An external focusingcoil 22 is provided. Thus, a low velocity electron scanning beam isdirected against the target plate 22. The electron beam may be alignedby an alignment coil. It is caused to scan the target plate 22 by meansof a deilecting yoke 24 which is supplied with sawtooth current from ade ilection circuit 36. If desired. spiral scanning may be employedinstead of sawtooth scanning.

The particular tube 2| being described by way of example is of the samedesign as the Image Orthicon employed for television pickup and,therefore, includes ring electrodes 21. and 2l for imaging the electronsfrom the photoelectric cathode 24 upon the target plate 22. This imagingof the electrons is caused by the electrostatic neld resulting from thering electron arrangement 31, 28 and by the electromagnetic ileld of thefocusing coil 32. Buch imaging is not essential for the use or thestorage tube 2| in the present invention as electrons from the cathode24 are utilized only to bring the target plate 22 to the potential ofthe screen 22 periodically as explained hereinafter.

In operation, as the scanning 4beam moves across the target plate 22 the`number oi velectrons in the return beam depends upon the potential4 ofthe target plate. Iithe scanning beam strikesa spot on target 22 that atmaximum positive potential, there will be a minimum lnum-- ber oielectronsin the return beam. The return beam releases secondaryelectrons from the end plate of the anode 2B and these electrons aredirected, by means of a persuader ring electrode '39, into a three-stageelectron multiplier 4I, 42, 43. The'electrons from the last stage strikea secondary electron emitting plate 44 and the resulting electrons goyto a screen electrode 4l whereby the output signal may be taken oir anoutput resistor 41.

The storage screen'or target plate 22 needv not be described in detail.However, it may be mentioned that a preferred target plate 22 is made ofvery thin glass, the glass being so thin that elemental areas of thelglass hold a charge for the desired length of time. Such a target plateis described in application Serial No. 631,441. illed November 28, 1941in the name of Albert Rose as a continuation oi lSerial No. 357,543,iiled September 20, 1940. now abandoned.

Referring more particularly to the circuit connections for the system o!Fig. 1, the signal trom 'the mixer Il is supplied through an .amplifier40. over a conductor 48 and through a blocking capacitor 49 to thescreen electrode -23 of the storage tube 2|. A steady bias voltage isapplied to the electrode 23 through a resistor 5I. Also. a square wavebias voltage 52 is applied from a square wave generator 52 through acoupling capacitor` 50 to the electrode 23. The square wave generator 53is synchronized with the modulating pulse generator I2. The deiiectioncircuit 36 is likewise synchronized with the generator I2.

At the endof every second scan of the scanning beam a pulse of light isllashed upon the photoelectric cathodel 24 whereby electrons fromcathode 24 bring the target plate 22 to the potential of the screenelectrode 23 because of the capacity between the plate 22 and lthescreen 23. The light pulse may .be obtained from any suitable source 54-which isvenergized from an electrical pulse'source il. The pulse sourceS3 is operated in synchronism with the modulating pulse generator I2. v.

The output signal ofthe storage tube 2| is taken oi! the resistor 4l andsupplied through a blocking capacitor 51 to an amplifier Il. Theamplified signal is supplied fromamplier vto thevertical deiiectingplates of avcathode ray oscilloscope 59.

The horizontal deiiecting plates of the oscilloscope 59 have a sawtoothvoltage wave applied to them from a deecting circuit Sito deilect theelectron beam of the oscilloscope along a time the oscilloscope Ilappears on the phosphores' cent screen (not shown) of the tube 59 unlessa blanking voltage is being applied to the oscilloscope control grid 62.

In the system illustrated, the square wave generator 53 supplies asquare wave blanking voltage to the oscilloscope grid 62 through anampliiler B3 with the wave of the correct polarity to block the electronbeam of the tube 59 during the first scan, i. e., during the scanimmediately following the pulse of light from source 54.

Figs. 2 and 3 illustrate the operation of the system shown in Fig. 1.Referring first to Fig. 2, the top graph represents the radio pulsesradiated from the transmitter antenna i6 and (in dotted line) the saidpulses received at the receiving antenna I1 after reflection from anobject which, in the presen-t instance, is assumed to be stationary. Thegraph 6B represents the sawtooth current that iiows through the storagetube deiiecting yoke 34 to produce the first scan and the second scan of'the target plate 22 by the scanning beam.

The graph 61 represents the light pulses that are produced at the end ofthe second scan and before the start of the first scan so that thecapacity elements of the target plate 22 are brought to a predeterminedpotential (1 volt in the present example) at the end of each cycleaofoperation.

The rectangular wave biasing voltage 52 of one volt peak-to-peak swingsthe mesh screen electrode 23 first one-half volt below its 11/2 voltfixed bias to one volt and then one-half volt above its xed bias to twovolts through the al.- ternating-current connection 50. This shift inthe potential of screen 23 will be seen by comparing the starting pointsof the graphs 1la and 12a.

'I'he graph B8 represents the sawtooth voltage applied to the horizontaldeflecting plates of the oscilloscope 59.

The graphs 1| and 12 represent the signals from the mixer I8 during Itheoccurrence of the received reflected pulses. The signals 1| and 12 arealsoA shown expanded in order to illustrate the operation of the storagetu-be more clearly.

The graphs 1| a and 12a show how the potential of the screen 23 varieswith the applied signai and bias. The graphs 1lb and 12b show that theglass target plate 22 varies in potential the same as the screen 23,this being due to the close spacing of the target plate 22 and thescreen 23. Since the potential of the gun cathode is fixed at ground,-this target plate potential is also theV voltage difference between thetarget plate and the cathode.

During the first scan, as the scanning beam moves along the targetpla-te from capacity element to capacity element the said capacityelements are being varied in potential by the screen 23 as shown at 1lb.The capacityv elements that are the more positive at the time thescanning beam strikes them will receivethe more electrons from the beam,its velocity being so low that the ratio of primary electrons tosecondary electrons is greater than unity. As a result, at the end ofthe first scan the charges on said scanned elements are represented bythe dotted-line graph 13.

During the second scan, as the scanning beam again moves over saidcapacity elements the target plate is being varied in potential the sameas before .by the signal on the screen 23, this target plate variationbeing represented at 12b. It

resented by graphs 12b and 13 are identical except that they are ofopposite polarity. Therefore. the net potential variation in saidcapacity elements as the beam scans along them is a zero variation asrepresented by the horizontal line 14. Thus, there is no'varlation inthe number of beam electrons deposited on the target plate and so asindicated at 1-6 there is no variation in lthe return beam. This meansthat the signal output at the output resistor 41 is zero and that noVindication will be produced on the screen of the oscilloscope 59 by thesignals reflected by the stationary object. Preferably, the outputsignal indicated at 11 that is produ-ced during the first scan isprevented from appearing on the os- 'cllloscope screen by blocking theoscilloscope scanning beam during the presence Aof the signal.

When a radio pulse is reflected from a moving object a signal willappear on the. oscilloscope screen. The operation of the storage tube inthis case is shown in' Fig. 3. Here the signals supplied from the mixerI8 during the first and second scan-s are represented by the graphs 8|and 82, respectively. Since the reected pulses producing these signalsare from a moving object such as an aircraft, the two signals are unlikefor reasons previously explained.

The potential of screen 23 is varied during lthe 'two scans as shown at8|a and 82a. 'I'he target plate is correspondingly varied in potentialas shown at 8|b and 82h. The potential left on the target plate at theend of the first scan is indicated at 83. The net instantaneouspotentials on the capacity elements as they -are scanned the second timeis shown by the graph 84. The

resulting output signal is indicated by -the graph 86. As previouslystated, the signal output produced during the first scan as indicated at81 is prevented from appearing on the oscilloscope by the blankingvoltage from amplifier 6 3.

From the foregoing it will be seen that the system of Fig. 1 willproduce an indication only when lthe reflection is from a moving object.More generally stated, the system distinguishes between successive likesignals and successive unlike signais.

As shown in Fig. 1A, the signals from the mixer I8 may be applied to thecathode 2E of the storage tube 2| by way of a lead 0| and an inputresistor 92 that is connected between the cathode and'ground. Likewise,the square wave biasing voltage may be applied to the cathode 26 by wayof a lead 93 and the lead 9|. The operation is the same as when thevoltage variation between l cathode and target plate is obtained byapplying signal to the mesh screen 23.

Fig. 4 shows an embodiment of the invention Where. instead 0f Varyingthe voltage difference between cathode and target plate, the number ofelectrons in the scanning beam is Varied. This modulation of the beam isproduced by applying will be seen that as a result of the signals 1| anda lead |04 to the amplifiers 40 and |02 to block amplifier |02 duringthe rst scan and Ito block amplier 4 0 during the second scan. Thus. asshown in Fig. 5, the scanning beam current is graph I 06.

During the second scan the signal passes through the reversing amplier|32 and the scanning beam is modulated as shown byY graph |01 of Fig. 5.1n the example illustrated the vilrst and second signals are unlikesince it is assumed that the pulses are reflected from a moving object.

At the start of the cycle of operation the targexl plate 2l is at twovolts potential'as shown by the graph 408, this lbeing the xed bias onthe mesh screen 23. During the iirst scan -the number of electronsdeposited on the successive capacity elements struck by the scanningbeam is las repre.. sented by the graph |09.` The resulting charge onsaid elements at the end of the rst scanis shown 1 by the graph I I; thegreaterA the 'number of elec#v trons deposited, the more negative thecharge.

-At the start of the second scan the-beam current is increased bythesquarev wave voltage sup- -plied over a conductor I2 to thecontrolelectrode 21 so that signal variations in either direction may bedetected. More specifically', vthe beam current is increased to avalueat thestart of the second scan such that there are alwaysmore thanenough electrons to bring the target plate to cath` ode potential. Asthe beam scans the target elements (which are charged as shown at lli)it v elements to cathode potential and also upon' thenumber of electronsin the scanning beam.

The number of electrons deposited during the second scan to bring thetarget plate to cathode potential is shown by the graph H2. It will be.

apparent that where the elements lof the-target plate are most negativethey take a minimum4 number of electrons to bring them to groundpotential. If the scanning beam contains `a reduced H3 to the amplifierIIS sov that signal is applied to the storage tube screen 23 during thefirst scan of the target plate 22 but not during the second scan. Also.square wave voltage from the generator 53 is applied over conductors llland Ill to the output amplliler 58 so that it is blocked during theiirst scan but passes signal during the second scan.

'In Fig. 8, the graph. |2| represents the signal applied to screenelectrode 23 during the rst scan. The resulting target plate potentialvariation is shown by graph |22. The return beam or outputsignal,represented by graph |23, is not passedby the amplier I3. During'thesecond sc'an the potential of the screen 23 is held at a steady biasvoltage as shown at |24. Due to the charges left on the target plate bythe nrst scan, yas shown at |23, the second scan produces the delayedoutput signal represented at |21.

l signal during the rst scan but not during the second scan as indicatedby the graphs |3| and |32 of Fig. 7. During the first scan the targetplate 22 remains at the screen potential of two volts as shown by graph|33 and the number of electrons l deposited during this scan is shown bygraph |34.

yThere is no output signal during the v:ilrst scan but sinc'e there maybe a certain amount of noise signal it may be desirable to block theoutput amplier 58 during this period.

During the second scan the charges leftvon the target plate elements bythe first scan, as shown at |38, cause a corresponding variation in the'electrons deposited during the second scan as shown at |31. TheVresulting return beam or delay output signal is shown at |33.

We claim as our invention: v

1. The method ofoperating a cathode ray storlage tubeof the type havinga targe't plate comnumber of electrons when it strikes these mostnegative elements, the number of return electrons will increase lessthan they otherwise would or will not increase at all. In the exampleshown, the rst part of the second signal is the same as the first partof the rst signal so that the return beam indicated at I3 is unchangedat rst. How

Aprising capacity storage elements which comprisesvarying the potentialof said target plate with reference to a fixed potential by a ilrstsignal as an 4electron beam scans capacity elements of said targetplate, varying the potential of said iula't'ed'` to` produce an -outputsignal only it said In the circuit of Fig. 4 the function of the lightand circuit diagram of Fig. 8, the storage tube 2| l may |be employedfor delaying a signal. In Fig. 8 the signal to be delayed is suppliedthrough an amplifier H6 and through a coupling capacitor ||1 to thescreen electrode 23. A square rwave voltage from the generator 53 issupplied over a conductor H3 and through a reversing amplifier twosignals are unlike. 4 I

- 2. The method of operating a cathode ray storage tube ot the'typehaving atarget plate comprising capacity Astorage elements whichcomprises storing a first signal Von said target plate as an electronbeam scans capacity elements of said target plate, varying the potentialof said target vplate with reference to a ilxed potential by a second`signal as said electron beam again scans said charged capacity elementswhereby the return beam from said target plate is signal modulated toproduce an output Signal only if said two signals are unlike, saidcapacity elements y `capacity element of` said mosaic when it is scannedby said beam is a function of said mosaic potential, means for causingsaid beam to scan said mosaic once while a signa`l is varying thepotential of said mosaic for causing the capacity elements of the mosaicwhich are thus scanned to acquire charges in accordance with thepotential variations of the mosaic with reference to said fixedpotential, means for causing said beam to scan said once-scannedelements a second time while an applied signal is again varying thepotential of said mosaic with reference to said xed potential whereby ifthe two signals are alike the voltage difference between the xedpotential point and successive scarmed capacity elements is constantduring said second scanning so that there is no signal output.

4. In combination, a cathode ray tube having a mosaic that functions tostore signals applied thereto, means for directing a beam of electronsagainst said mosaic, means for varying the potential of said mosaic withrespect to a fixed reference potential and in accordance with an appliedsignal whereby the charge acquiredby a capacity element of said mosaicwhen it is scanned by said beam is a function of said mosaic potential,means for causing said beam to scan said mosaic once while a signal isvarying the potential of said mosaic for causing the capacity elementsof the mosaic which are thus scanned to acquire charges in accordancewith the potential variations of the mosaic with reference to saidi'lxed potential, means for causing said beam to scan said oncescannedelements a second time while an applied signal is again varying thepotential of said .mosaic with reference to said fixed potential wherebya signal output is obtained from the return beam only if there is adifference in said two applied signals, said mosaic being brought to apredetermined potential before the next cycle of operation.

5. The method of operating a cathode ray storage tube having a targetplate comprising capacity storage elements and having an electron gunwhich comprises causing a low velocity electron beam from said gun toscan capacity elements of said target plate a iirst time and a secondtime, causing said electron beam to charge said scanned capacityelements at least during the rst scan in accordance with a signalapplied to said storage tube whereby the return beam from said targetplate is signal modulated during the second scan unless a signal likethe rst signal is applied to said tube during the second scan, returningthe capacity elements of said target Plate to a predetermined potentialat the end of the second scan, and repeating the cycle of operation.

6. In combination, a cathode ray storage tube having a target platecomprising capacity storage elements and having an electron gun, meansfor causing a low velocity electron beam from said gun to scan capacityelements of said target plate a first time and a second time, means forcausing said electron beam to charge said scanned capacity elements atleast during the ilrst scan in accordance with a signal applied to saidstorage tube whereby the return beam from said target plate is signalmodulated during the second scan unless a signal like the rst signal isapplied to said tube during the second scan, and means for returning thecapacity elements of said target plate to a predetermined potential atthe end of the second scan and before the cycle of operation isrepeated.

7. The invention according to claim 6 wherein said last means comprisesa photoelectric cath- 0de positioned to release electrons toward saidtarget plate, and further comprising means for flashing light upon saidphotoelectric cathode at the end of the second scan and before the cycleof operation is repeated whereby electrons fall upon said target plateto return it to said predetermined potential.

8. In combination, a cathode ray tube having a. double-sided mosaic thatfunctions to store signals vapplied thereto, means for directing a beamof low velocity electrons against said mosaic, a fine mesh screenpositioned close to said mosaic in capacitive relation thereto wherebythe charge acquired by a capacity element of said mosaic when it isscanned by said beam is a function of the potential of said mesh screenand of the number of electrons in said beam, means for causing said beamto scan said mosaic once and for simultaneously causing the capacityelements of the mosaicwhich are scanned thereby to acquire charges inaccordance with the variations of a signal applied to said tube, meansfor causing said beam to scan said once-scanned elements a second timewhile a signal is again being applied to said tube whereby a signaloutput is obtained from the return beam only if there is a difference insaid two applied signals, and means for bringing said mosaic to the biaspotential of said mesh screen at the end of said second scan and beforethe next first scan begins.

9. In combination, a cathode ray tube having a double-sided mosaic thatfunctions to store signals applied thereto, means including an electrongun for directing a beam of low velocity electrons against said mosaic,said electron gun including a cathode, a fine mesh screen positionedclose to said mosaic in capacitive relation thereto whereby the chargeacquired by a capacity element of said mosaic when it is scanned by saidbeam is a function oi the potential difference of said mesh screen andsaid cathode and of the number of electrons in said beam, means forcausing said beam to scan said mosaic once and for simultaneouslyvarying the voltage difference between said mesh screen and cathode inaccordance with a signal for causing the capacity elements of the mosaicwhich are scanned by said beam to acquire charges in accordance with thevariations of sai-d signal, means for causing said beam to scan saidonce-scanned elements a. second time while a signal is again varyingsaid voltage difference whereby av signal output is obtained from thereturn beam only if there is a difference in said two applied signals,and means for bringing said mosaic to the bias potential of said meshscreen at the end of said second scan and before the next first scanbegins.

10. In combination, a cathode ray tube having a double-sided mosaic thatfunctions to store signals applied thereto, means including an electrongun for directing a beam of low velocity electrons against said mosaic,said electron gun including a cathode, a fine mesh screen posi tionedclose to said mosaic in capacitive relation thereto whereby the chargeacquired by a capacity element of said mosaic when it is scanned by saidbeam is a function of the potential diierence of said mesh screen andsaid cathode and of the number of electrons in said beam, means forcausing said beam to scan said mosaic once and for simultaneouslyvarying the voltage difference between ysaid mesh screen and cathode inaccordance with a signal for causing the capacity elements of the mosaicwhich are scanned by said beam to acquire charges in ac- :,ssnooscordance with the variations of said signal, means for causing said beamto scan said oncescanned elements a second time while a signal is againvarying said voltage diercnce whereby a signal output is obtained fromthe return beam only if there is a difference in said two appliedsignals, and means for bringing said mosaic to the bias potential ofsaid mesh screen at the end of said second scan and before the next rstscan begins, said last means comprising a photoelectric cathode andmeans for projecting a pulse of light thereupon between the end of thesecond scan and the beginning of the following first scan.

1l. The method of operating al cathode ray storage tube having a targetplate comprising capacity storage elements and having an electron gunthat includes acatho'de which comprises storing a first signal on saidtarget plate as a low velocity electron beam from said gun scanscapacity elements of said target plate, varying the voltage differencebetween said cathode and said target plate by a second signal as saidelectron beam again scans said capacity elements whereby the return beamfrom said target plate is signal modulated only if said two signals areunlike, returning the capacity elements of said target plate toafpredetermined potential at the end of the second scan, and repeatingthe cycle of operation.

12. In combination, a cathode ray storage tube having a target platecomprising capacity storage elements and having an electron gun thatincludes a cathode, means for storing a rst signal on said target plateas a low velocity electron beam from said gun scans capacity elements ofsaid target plate, means for varying the voltage dinerence between saidcathode and said target plate by a second signal as said electron beamagain scans said capacity elements whereby the return beam from saidtarget plate is signal modulated only if said two signals are unlike,and means for returning the capacity elements of said target plate to apredetermined potential at the end of the second scan and before thecycle of operation is repeated.

screen, means for causing said beam to scanv said once-scanned elementsa second' time while ,Y

a signal is again being applied to said mesh screen whereby a signaloutput is obtained from the return beam only if there is a diiierence ina double-sided mosaic that functions to store` signals applied thereto,means for directing a beam of low velocity electrons against said mosa-13. vThe method of operating a cathode ray f storage tube of thelowrvelocity beam type having a target plate comprising capacity storageelements which comprises storing a vilrst signal on said target plate asa 'low 'velocity electronl beam scans capacity. elements .of said targetplate, varying the potential of said target plate by a second signalassaid electron beam vagain scans said capacity elements whereby thereturn beam from saidtar'get. plate is signal modulated only if said twosignals are unlike, returning the vcapacity elements of said targetplate to a pre--l determined potential at the end of the second scan,and repeating the cycle of operation.

14. In combination, a cathode ray vtube having a double-sided mosaicthat functions to store signals applied thereto, meansfor directing abeam of low velocity .electrons against said mosaic, a une mesh screenpositioned' close to said mosaicjin capacitive relation thereto wherebythe charge4 acquired by a capacity element of said mosaic when it isscanned by said beam is a function of the potential of said mesh screenand of the number of electrons in said beam, means for causing said beamto scan said mosaic once and for simultaneously causing the capacityelements of the mosaic which. are scanned thereby to acquire charges inaccordance with the variations of a signal appliedto said mesh ic, ailne mesh screen positioned close to said mosaic in capacitive relationthereto whereby the charge acquired by a capacity element of said mosaicwhen it is scanned by said beam is a function of the potential of saidmesh screen and of the number of electrons in said beam, means forcausing said beam to scan said mosaic once and for simultaneouslycausing the capacity elements of the mosaic which are scanned thereby toacquire charges in accordance with the variations of a signal applied tosaid mesh screen, means for causing said beam to scan said once-scannedelements a second time while a signal is again being applied to saidmesh screen whereby a signal output is obtained from the return beamonly if there is a dii'i'erence in said two applied signais, and meansfor bringing said mosaic to the lbias potential of said mesh screen atthe end of said second scan and before the next first scan begins, saidlast means comprising a photoelectric cathode positioned to releaseelectrons toward said target plate and means for projecting a pulse oflight thereupon between the end of the second scan and the beginning ofthe following first scan.

16. In combination, a cathode ray tube having a double-sided mosaic thatfunctions to store signals applied thereto, means including a beamintensity control electrode for directing a beam oi' low velocityelectrons against said mosaic, a ilne mesh screen positioned close tosaid mosaic in capacitive relation thereto wherey the charge acquired bya capacity element of said mosaic whenit is scanned by said beam is afunction of the potential of said mesh screen and of the number ofelectrons in said beam, means for causing said beam to scan said mosaiconce and for simultaneously causing the capacity elements of the mosaicwhich are scanned thereby to acquire charges in accordance with thevariations of a signal applied to said control electrode with a certainpolarity, meansv for causing said beam to scan said once-scannedelements la second time while a signal is again being applied to'saidcontrol .electrode with the opposite polarity whereby e a signal outputis obtained from the return beam v said capacity elements whereby thereturn beam from said target plate is modulated in accordance with saidstored signal to produce a delayed signal. returning the capacityelements ofsaid tar- 13 get plate to a, predetermined potential at theend of the second scan, and repeating the cycle of operation.

18. The method of operating a cathode ray storage tube having a targetplate comprising capacity storage elements and having an electron gunwhich comprises storing a signal on said target plate only While a 10Wvelocity electron beam from said gun scans capacity elements of saidtarget plate duringa, rst scan, again scanning said capacity elementswhereby the return beam from said target plate is modulated inaccordance with said stored signal to produce a delayed signal,projecting electrons upon the capacity elements of said target plate tobring them to a. predetermined potential at the end of the second scan,yand repeating the cycle of operation.

PAUL K. WEIMER. VLADIMIR. K. ZWORYKIN. IRVING WOLFF.

No references cited.

